Method of generating a signal to indicate a curve

ABSTRACT

The differences ΔV of the speed signals of diagonally opposed wheels and the time variation signals of these differences are formed. If at least one of these signals exceeds a prescribed threshold, a curve detection signal is supplied which can be used to shut down the delay of the yaw speed build-up in an ABS.

BACKGROUND OF THE INVENTION

German DS 34 21 700, to which U.S. Pat. No. 4,593,955 corresponds,discloses an anti-lock brake control system which includes sensors, anevaluation circuit and brake pressure controls. The front wheels areindividually controlled, but there is a delay of the yaw torque build-upat a front wheel running on a surface with a higherμ (high wheel) with astart of the control, this delay slows down the pressure build-up at afront wheel running on a surface with a lowerμ (low wheel). The purposeof this measure is to slow down the generation of yaw torques around thevertical vehicle axis on road surfaces with an asymmetric frictioncoefficient such that the vehicle remains under controlled operation.

This delay of yaw torque build-up, however, is disadvantageous when avehicle passes a curve and during the then following control for tworeasons. First, a vehicle which is subject to braking exhibits in thecurve a rotation into the circle. Second the delay of the yaw torquebuild-up causes the generation of a counter-directed torque to bedelayed because of the immediate full braking effect at the front wheelat the outer edge of the curve. Said publication therefore proposes toshut off the delay of the yaw torque build-up in a curve and toindividually control the pressure in the wheel brakes of the frontwheels. A transverse acceleration sensor is used to detect the curves.

It is disadvantageous that a transverse acceleration sensor must be usedwhich in turn requires additional monitoring means.

SUMMARY OF THE INVENTION

Assuming that wheel speed sensors are provided for different reasons(e.g. ABS), a curve can be detected without additional sensors bymeasuring the speed difference of diagonally opposed wheels andgenerating a signal corresponding to this difference or the variation ofthis difference with time. When at least one of these signals exceeds aprescribed limit, a signal which indicates the curve is generated.

The so recovered curve signal can be used, for example, to shut off thedelay of the yaw torque build-up, to switch slippage- and accelerationthresholds in the evaluation circuit and also to monitor the transverseacceleration sensor.

During steady speed through a curve even without braking, there is aspeed difference in at least one diagonal. In a left curve, the diagonalleft front wheel/right rear wheel of a rear-wheel-driven vehicleexhibits such a difference. In case of a front wheel drive vehicle,under the same conditions, it is just the opposite diagonal. In a rightcurve, the diagonal right front wheel/left rear wheel of a rear wheeldrive vehicle exhibits the difference, while it is the opposite diagonalfor a front drive vehicle.

Using only the speed difference, it is advantageous, to signal the curvedetection only after the difference has been present for a certainperiod of time. This time varies for different types of vehicles and ison the order of several hundred milliseconds. The threshold for ΔV,after which there is a difference sufficient for curve detection, alsodepends upon the vehicle type. It ranges in the magnitude of 1-3 km/h.It appears advantageous to set the threshold such that curve detectionstarts at a transverse acceleration of approximately 0.5 g.

It also turned out that during unsteady speed in a curve, there arevariations in the rotational speed difference. These too can be used forcurve detection. Advantageously, both signal types are used together.The above mentioned monitoring period for the speed difference can thenbe reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram in accordance with the invention and the useof the curve detection signal for shutting down the delay of the yawtorque build-up.

FIG. 2 is additional possibility of application.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows four sensors for measuring the wheels speeds which arereferenced as LF (left/front), RF (right/front), LR (left/rear) and RR(right/rear). The signals of the sensors belonging to a diagonal areconnected to a respective subtractor 1, 2. The differences ΔV aresupplied to blocks 3 and 4 where change signals in dependency upon timeare formed.

In comparators 6 and 8, the speed differences ΔV are compared to firstthreshold values. In comparators 5 and 7, the change signals arecompared to second threshold values. If a comparator 5 or 6 or 7 or 8determines that a threshold has been exceeded, it supplies a signal, anda monostable element 12 with a prescribed time constant is set via theOR-gates 9 and 10 and via an OR-gate 11. The output signal thereof issupplied to the evaluation circuit 13 of an ABS where it shuts down thedelay of the yaw torque build-up. After the signal supplied by one ofthe OR-gates 9 and 10 is terminated, and after the time constant of themonostable element 12 has elapsed, the shut down of the delay of the yawtorque build-up is terminated unless an ABS-control procedure is beingexecuted.

In FIG. 2 it is assumed that a transverse acceleration sensor 20 is usedfor the shut down via a terminal 21 and that the signal of the OR-gate11 is used for monitoring this transverse acceleration sensor 20. Forthis purpose, the signals which indicate a curve are supplied to acomparator 22. The latter supplies a warning and/or shut-down signal viaterminal 23 when a curve is detected via the arrangement of FIG. 1without the release of a corresponding signal by the transverseacceleration sensor 20.

We claim:
 1. Method for controlling yaw torque build-up in a vehiclehaving two front wheels and two rear wheels in diagonally opposed pairsand equipped with an anti-lock brake control system wherein the brakepressure at said front wheels is individually controlled to delay theyaw torque build-up when one front wheel runs on road surface having ahigher friction coefficient than the other front wheel by slowing downthe pressure build-up at the front wheel running on the surface with alower friction coefficient, said method comprisingmeasuring the speedsof the four wheels, calculating the difference of the speeds of thewheels in each pair of diagonally opposed wheels to produce twodifference values Δv, comparing said difference values Δv to firstprescribed threshold values, generating a signal indicative of thevehicle passing through a curve when one of said first threshold valuesis exceeded, and shutting down the delay of yaw torque build-up whensaid signal is generated.
 2. Method for controlling yaw torque build-upin a vehicle having two front wheels and two rear wheels in diagonallyopposed pairs and equipped with an anti-lock brake control systemwherein the brake pressure at said front wheels is individuallycontrolled to delay the yaw torque build-up when one front wheel runs onroad surface having a higher friction coefficient than the other frontwheel by slowing down the pressure build-up at the front wheel runningon the surface with a lower friction coefficient, said methodcomprisingmeasuring the speeds of the four wheels, calculating thedifference of the speeds of the wheels in each pair of diagonallyopposed wheels to produce two difference values Δv, calculating thechange in Δv for each pair of diagonally opposed wheels over time toproduce change values dΔv/dt, comparing said change values dΔv/dt tosecond prescribed threshold values, generating a signal indicative ofthe vehicle passing through a curve when said one of second thresholdvalues is exceeded, and shutting down the delay of yaw torque build-upwhen said signal is generated.
 3. Method for controlling yaw torquebuild-up in a vehicle having two front wheels and two rear wheels indiagonally opposed pairs and equipped with an anti-lock brake controlsystem wherein the brake pressure at said front wheels is individuallycontrolled to delay the yaw torque build-up when one front wheel runs onroad surface having a higher friction coefficient than the other frontwheel by slowing down the pressure build-up at the front wheel runningon the surface with a lower friction coefficient, said methodcomprisingmeasuring the speeds of the four wheels, calculating thedifference of the speeds of the wheels in each pair of diagonallyopposed wheels to produce two difference values Δv, comparing saiddifference values Δv to first prescribed threshold values, calculatingthe change in Δv for each pair of diagonally opposed wheels over time toproduce change values dΔv/dt, comparing said change values dΔv/dt tosecond prescribed threshold values, generating a signal indicative ofthe vehicle passing through a curve when one of said threshold values isexceeded, and shutting down the delay of yaw torque build-up when saidsignal is generated.